1. Field of the Invention
The subject matter of the present application relates to electrical antifuses, especially such devices provided in integrated circuit chips.
2. Description of the Related Art
Integrated circuit chips often include elements which can be permanently altered after manufacture in order to make certain changes to circuits therein, or to maintain states or data on the chip. For example, an integrated circuit chip can include electrically operable fuses or an array of fuses to store critical information on chip, to conduct redundancy repair to improve manufacturing yield, or to fine tune circuit performance through local circuit trimming, among other purposes. Such fuses initially begin as conductive elements, i.e., devices which are closed circuit in that initially, they are electrically connected between external terminals. A fuse can be programmed, i.e., blown, to make it much less conductive, i.e., open circuited in that it effectively is no longer electrically connected between external terminals. Electrical antifuses are alternative structures which can be provided on an integrated circuit. Such antifuses typically begin as elements which are essentially nonconductive, having high electrical resistance (i.e., open circuit state). Programming an antifuse greatly reduces the electrical resistance of the antifuse to a level at which the antifuse is electrically connected between external terminals, achieving in effect a closed circuit state.
One challenge faced by electrical fuses and antifuses used in integrated circuit chips is the ability to reliably program the fuse or antifuse. During programming, an electrical fuse may require a metal fuse link to melt under high current, which can cause local explosion with metal particles scattered far away from the blown fuse or stress cracks to form in adjacent dielectric materials and affect nearby circuits. In some existing electrical antifuses, a high voltage is applied across a thin dielectric layer to create a localized breakdown that is electrically conductive. These types of fuses and antifuses can sometimes fail to change completely to a programmed state, such that a fuse can remain relatively conductive even after programming, and an antifuse may remain too resistive after programming. In some cases, only 90-99% of these devices work properly when programmed. Another challenge for many of the fuse or antifuse solutions today which utilize such destructive mechanisms is the ability to maintain the programmed state of the fuse or antifuse throughout its useful life time. In aggravated application environments such as high temperature, some programmed fuses and antifuses may gradually change back into their previous unprogrammed states.
Moreover, fuses and antifuses may require special high voltage levels not available on the integrated circuit chip for programming them. This can pose design challenges for supplying the voltage levels on the chip and contributes to the overall cost of making the chip.